The Classic is constructed of 600D Hydrotuff material, a UV resistant, waterproof PVC backed polyester. The bag is made from one big piece of material with seams only on its two sides. Its patented design closes like a white water rafting bag to keep water out. If you would like to be 110% sure, you can add the PackRight waterproof liner. Sewn in loops accommodate the PackRight Security Cable Lock. The Classic Carrier can be used on vehicles with or without roof racks-please see the Classic Set Up Guide for details.